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Academic Evidence On R1/r2 Colour

Discussion in 'Blu-ray & DVD discs' started by howard444, Jun 22, 2005.

  1. howard444

    howard444
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    I have decided to create this fresh thread so that all those involved in the discussion that I instigated over R1 V R2 and the ins and outs of NTSC and PAL can read the objective academic evidence that I did not include in my subjective postings.

    The following information was transcribed by me during a phone conversation with SALFORD UNIVERSITY Lecturer
    John Bingham.

    " We should start with the basics. Both 60hz aka NTSC and 50hz aka PAL in the Region 1 and Region 2 DVD format have the exact same horizontal resolution.

    720 PIXELS across the screen

    This is HORIZONTAL resolution and is the same for both
    standards.

    While 50hz/PAL has 576 active lines as VERTICAL resolution

    While 60hz/NTSC has 480 active lines as VERTICAL resolution.

    To fit into an standard definition DVD capacity, memory is assigned in chips in terms of a power of 2. The basic unit is 1 MEGABIT. That is not a million but 2 to the power of 20.

    1048576 Memory locations
    that being 1 Megabit of memory.

    When decoding one seeks to fit a complete video frame into a simple multiple of the above number.

    What is normally used is 4 MEGABITS.

    4194304 Memory locations
    This is the basic video frame within the DVD format.

    Now, totally uncompressed video, which gives you 8 Bits for each of the RGB colours is normally stored in what is called

    4:4:4 format
    This is pure uncompressed component video
    Y,Cr,Cb or sometimes known as YUV format.

    Our eyes are very sensitive to brightness/luminance details but not as senstive to colour detail.

    So the normal broadcast quality standard is to work at

    4:2:2 format
    This means that half the fine detail in the colour
    has been lost as the viewer is less conscious of
    this lost colour detail.

    But this is still not enough data reduction to allow a small amount of memory to be used in domestic/consumer applications.

    So for 60hz/480line DVD aka NTSC the colour detail is reduced by a further factor of 2 to give...

    4:1:1 format
    This means that there is 1Bit of red difference and
    1Bit of blue difference, component information for
    every 4 bits of luminance information.

    At 8 Bit (luminance) video depth this means a
    complete video frame of 480 x 720 Pixels.

    4147200 Memory locations
    this is just below 4 Megabits.
    One 4 megabit block of memory can hold one
    complete frame.

    This is NOT POSSIBLE with 50hz / 576 line PAL !!!!!

    As a single frame would then require...

    4976640 Memory locations.

    So to reduce the information back to just below 4 Megabits per frame for a PAL/ REGION 2 DVD the colour detail information is again reduced by half to give what is known as

    4:1:0 format

    The DVD format again requires...

    4147200 Memory locations
    as required per frame by the
    60hz/480 line NTSC standard.

    Both standards therefore only require just under 4 Megabits for a complete video frame.

    The ZERO in: 4:1:0 spec on R2/ 50hz / PAL DVD
    represents a further loss in colour detail.

    In conclusion.

    At the end of the day the final result is this.

    Both standards have identical HORIZONTAL resolution.

    The PAL standard has 20% greater VERTICAL resolution
    for fine brightness detail. BUT...

    This is at the LOSS of 50% of the colour fine detail !!

    Therefore on PAL / 576 line / 50hz

    7/8th's of the total fine-colour-detail is lost from each
    frame.

    John Bingham
    Salford University "

    Written to site by Howard Simon Marks.
     
  2. Mr.D

    Mr.D
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    sigh. DVD is 4:2:0 . It can be 4:1:1 but never is on a commercial dvd. 4:1:0 is used for video conferencing and low bandwidth video.

    4:1:1

    In 4:1:1 chroma subsampling, the horizontal color resolution is quartered. This is still acceptable for lower-end and consumer applications. Uncompressed video in this format with 8-bit quantization uses 6 bytes for every macropixel (4 pixels in a row).

    Mapping:

    The bitstream

    Y0 U0 Y1 Y2 V2 Y3

    will map to the following four pixels:

    [Y0 U0 V2] [Y1 U0 V2] [Y2 U0 V2] [Y3 U0 V2]

    Formats that use 4:1:1 chroma subsampling include:

    * DVCPRO
    * NTSC DV and DVCAM
    * D-7

    4:2:0

    4:2:0 does not mean that there is no V or Cb information stored at all, it means that in each line, only one color difference channel is stored with half the horizontal resolution. The channel which is stored flips each line, so the ratio is 4:2:0 for one line, 4:0:2 in the next, then 4:2:0 again, and so on. This leads to half the horizontal as well as half the vertical resolution, giving a quarter of the color resolution overall. The PAL and SECAM color systems are especially well-suited to this kind of data reduction. Uncompressed video in this format with 8-bit quantization uses 6 bytes for every macropixel (2×2 pixels).

    Mapping:

    The bitstream

    Yo0 Uo0 Yo1 Yo2 Uo2 Yo3

    Ye0 Ve0 Ye1 Ye2 Ve2 Ye3

    will map to the following two lines of four pixels each:

    [Yo0 Uo0 Ve0] [Yo1 Uo0 Ve0] [Yo2 Uo2 Ve2] [Yo3 Uo2 Ve2]

    [Ye0 Uo0 Ve0] [Ye1 Uo0 Ve0] [Ye2 Uo2 Ve2] [Ye3 Uo2 Ve2]

    The quality of this method is very close to 4:1:1, and it is used in the following formats:

    * DVD and other Main Profile MPEG-2 implementations
    * PAL DV and DVCAM
    * most common JPEG and MJPEG implementations

    4:1:0

    This ratio is possible (indeed, some codecs do support it), but not widely used, since its color fidelity is even below that of VHS. It means half the vertical and quarter the horizontal color resolutions, with only one eighth of the bandwidth of the maximum color resolutions used. Uncompressed video in this format with 8-bit quantization uses 10 bytes for every macropixel (4 x 2 pixels).

    Mapping:

    The bitstream

    Yo0 Uo0 Yo1 Yo2 Yo3

    Ye0 Ve0 Ye1 Ye2 Ye3

    will map to the following two lines of four pixels each:

    [Yo0 Uo0 Ve0] [Yo1 Uo0 Ve0] [Yo2 Uo0 Ve0] [Yo3 Uo0 Ve0]

    [Ye0 Uo0 Ve0] [Ye1 Uo0 Ve0] [Ye2 Uo0 Ve0] [Ye3 Uo0 Ve0]
     
  3. Mr.D

    Mr.D
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    Your friend might be getting confused by the fact that if you try to generate 4:2:0 from 4:1:1 you end up with 4:1:0 because you effectively end up with an empty sample because of how 4:2:0 is distributed. This doesn't happen with dvd ( or broadcast mpg or domestic DV formats) as the 4:2:0 is derived from 4:2:2 or higher.

    I'm getting a bit bored now.
     
  4. ad47uk

    ad47uk
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    How many people would notice the difference? I am not an expert by a long way and I do not pretend I know what the hell any of you are on about, but at the end of the day, people gets the DVD, stick in into their DVD player and watch it. The quality is better than VHS and that is all people are worried about. It is pointless worrying about chroma subsampling or any other tech word.

    I got a mate who is a video editor and cameraman and he knows about all this stuff, but as he said to me, the normal public don't and should not know anyway.

    At the end of the day you sit down, watch a DVD and thast is it. As been said either on this thread or the other thread, to notice the difference, most people would have to have a DVD in R1 and the same one in R2 and watch them both together to notice the difference.

    So stop watsing your lifes on this and do something more interesting, it is a nice sunny day and I am going to go outside and dig the garden.
     
  5. Mr.D

    Mr.D
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    Noticing something and finding it objectionable are seperate issues.
    The entire point of this discussion was to highlight what are in fact merely differences between the two types of video commonly found on commercial dvds ( 625/50 and 525/60).

    Both have their pros and cons but I take exception to someone proclaiming either is better than the other especially when they back it up with a load of erronious piffle. Those of us who take interest is such things regarded the whole issue as being laid to rest years ago.

    If the differences don't bother you thats great.

    I have to say I'm not particularly bothered one way or the other myself but thats not the same as being unaware of the characteristics of either format.

    And this forum is for enthusiasts who tend to analyse image criteria with more rigour than your average punter.
     
  6. Steve.J.Davies

    Steve.J.Davies
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    If we step back from deep techno doesn't it come down to down which one you prefer looking at ?
     
  7. Mr.D

    Mr.D
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    Thread isn't about personal preference. I'm sure some people in the world "prefer" watching vhs for all the relevance that's worth.
     
  8. Steve.J.Davies

    Steve.J.Davies
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    "And this forum is for enthusiasts who tend to analyse image criteria with more rigour than your average punter."
    Fair enough - we all set our own criteria. I stick to viewable ones and compatibility ones so that I can make the judgement and decisions that make criteria criteria to me.
    e.g. how many bytes per macropixel (et al) don't fall into my criteria but they do yours - I can live with that. Your list and relative importance is yours and mine is mine.
    Uniformity = boredom so I am agin it.
     
  9. Mr.D

    Mr.D
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    You may want to take notice of the fact that I did not instigate this thread. I'm merely responding to the erronious mewlings of an individual who sought to preach to the forum about matters he was clearly unable to express adequately or even correctly.
     

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